In both oxide and non-oxide metal and ceramic materials, impurities such as halogens, especially chlorine and fluorine, can evolve as a gas during sintering of the materials, as can oxygen impurities in non-oxide metals and ceramic materials. Such evolved gases may react with the metal or ceramic materials to form one or more secondary gaseous species containing one or more of the constituent elements of the metal or ceramic material, thus effectively raising the vapor pressure of the metal or ceramic material, where “vapor pressure” refers to the total partial pressure of all gaseous species containing cation(s) of the sintering material. This can in turn lead to evaporation/condensation coarsening of the microstructure. Uneven evaporation/condensation coarsening of the microstructure during sintering can cause density gradients to form in the material, e.g. to a more dense exterior than interior, and limit the densities attainable. Ness & Rafaniello, J. Am. Cer. Soc., 77:2879-2874 (1994); portions of Sweeney, “Permeability, Drying, and Sintering of Pressure Filtered Ceramic Nanopowders”, Ph.D. Thesis, The Pennsylvania State University, 2005; and U.S. Pat. No. 2,834,651, the contents of all of which are incorporated herein by reference, are believed to represent relevant prior art.